Heretofore, single-color tapered testers for small disposable batteries had a single elongated thermo-responsive element extending along a resistive heater strip. A taper in the heater strip created a test current density gradient which produced a corresponding test equilibrium temperature gradient along the active area. These tapered testers normally employed a single LCD (liquid crystal display) element mounted over the temperature gradient next to a status scale. The LCD had a single response temperature. The user determined the status of the battery by observing the point on the scale where the increasing equilibrium temperature along the temperature gradient was equal to the fixed response temperature of the LCD. Mis-registration of the status scale along the temperature gradient reduced the accuracy of the testing. The following U.S. patent issued to Robert Parker teach tapered battery testers: U.S. Pat. No. 4,006,414 issued on Feb. 1, 1977; U.S. Pat. No. 4,702,563 issued on Oct. 27, 1987; U.S. Pat. No. 4,702,564 issued on Oct. 27, 1987; U.S. Pat. No. 4,726,661 issued on Feb. 23, 1988, and U.S. Pat. No. 4,737,020 issued on Apr. 12, 1988.
Prior multi-element testers for small disposable batteries had a series of thermo-responsive elements spaced the along the tester in a series of adjacent sites. The thermo-responsive elements had progressively higher activation temperatures which indicated the status of the battery. The large interface area between the series of elements and the body of the battery permitted heat loss from the tester into the battery. This heat loss increased the response time of the tester, and reduced the test temperature. U.S. Pat. No. 4,835,475 issued on May 30, 1989 to Niichi Hanakura shows such a multi-site, multi-element configuration.
A single element, sliding contact tester is shown in U.S. Pat. No. 5,231,356 issued on Jul. 27, 1993 to Robert Parker (Ser. No. 07/899,371, filed Jun. 16, 1992). The operating length of the resistive heater strip is manually decreased during the testing by pulling on one end of the tester causing a sliding contact between the heater and one terminal of the battery. The lower electrical resistance of the shortened heater permits the lower current from partially expired batteries to activate the thermo-responsive element.